In recent years, there has arisen a need for high-performance polymeric materials in the development of electronic devices such as liquid-crystal displays, organic electroluminescence (EL) displays, touch panels, optical semiconductor devices (LEDs), solid-state image sensors, organic thin-film solar cells, dye-sensitized solar cells and organic thin-film transistors (TFTs).
The specific properties desired in such polymeric materials include (1) heat resistance, (2) transparency, (3) high refractive index, (4) high solubility, (5) low volume shrinkage, (6) resistance to high temperatures and high humidity, and (7) high film hardness.
The inventors earlier discovered that hyperbranched polymers containing recurring units with a triazine ring and an aromatic ring have a high refractive index, are capable of achieving, with the polymer alone, high heat resistance, high transparency, high refractive index, high solubility and low volume shrinkage, and are thus suitable as film-forming compositions in the manufacture of electronic devices (Patent Document 1).
The inventors also earlier discovered that, when reacting a benzenetricarboxylic acid with a diamine to produce a hyperbranched aromatic polyamide, those aromatic polyamides obtained by adding a monofunctional substance capable of reacting with carboxyl groups, etc. on the benzenetricarboxylic acid so as to cap some of the reactive end groups and thereby control hyperbranching have a good solubility in organic solvents while retaining heat resistance and transparency, and thus can be advantageously used as the base polymer of film-forming compositions when producing electronic devices (Patent Document 2).
However, in both above hyperbranched polymers, to achieve a high film hardness, it is essential to increase the crosslink density by using a crosslinking agent. Unfortunately, in aromatic polyamide-based hyperbranched polymers, adding a crosslinking agent often lowers the refractive index and heat resistance. Moreover, because this polymer uses carboxyl groups bonded directly to the benzene ring as the crosslink sites, the crosslink reactivity is low and the range of choice in crosslinking agents is narrow, in addition to which the cured product has a low crosslink density and cracks sometimes arise. When the polymer is formed into a thin-film, other problems include a tendency to absorb water and inadequate alkali resistance. Depending on the intended application, improvements in these areas are sometimes desired.
And in triazine ring-containing hyperbranched polymers, adding a crosslinking agent not only lowers the refractive index, it also makes it impossible to obtain a film having the high degree of hardness that is anticipated.